1. Field of the Invention
This invention relates to improvements in determining the test weight of grain, and more particularly for doing it automatically, accurately and inexpensively.
2. Prior Art
The test weight per bushel of grain (usually shortened and referred to as "test weight") is an important factor in assigning a grade to a lot of grain under the official grain standards of the United States. It is therefore essential that the test weight per bushel be accurately determined as it affects the market value of the grain.
An apparatus for determining test weight per bushel for grain was designed by the U.S. Department of Agriculture for determining test weight per bushel of various grains. This standard weight-per-bushel tester is described in Circular 921 June 1953 USDA which superseded USDA Bulletin 1065 issued May 1922. The apparatus includes a stand, a filling hopper, a test kettle, a weighing beam, an overflow pan and a stroker. The user pours about one and one-fourth quarts of grain into the filling hopper that has a stopper in its base. The bottom of the hopper is two inches above a one-quart cylindrical test kettle. The stopper is released and the grain flows through the hopper overflowing the test kettle. The operator then uses the standard stroker to level the grain along the top of the test kettle and then he weighs the container on a beam scale. The use of this USDA designed standard test weight apparatus is clumsy, slow and inefficient in the use of personnel even though it is accurate and it is the legal standard. There has been a long-standing need in the art to provide test weight per bushel automatically, inexpensively and with as much accuracy as the USDA standards apparatus, but without the deficiencies as outlined above.
In measuring "test weight" (generally defined as volume of grain divided by its weight) three different types of errors are encountered, namely, errors in measuring volume, errors due to compaction, and errors in measuring weight. As to errors in measuring volume, if it is assumed that a cross-sectional area is known in constant then this error is only a function of the accuracy in measuring height. In the USDA legally accepted procedure, described above, this error in height is negligible for two reasons: (1) a large cup is used, thus a small error in height is negligible in calculating cup volume and, (2) by pushing a leveling stick across the top surface of the cup, error in height is minimal. Errors due to compaction occur since grain kernels vary significantly in size and shape and the amount that can fit into a fixed volume can also vary considerably. In the USDA test weight procedure this compaction error is minimized by loading the cup from a fixed geometry funnel located a fixed distance above the cup. Errors in weighing accuracy obviously would cause an error in the test weight. In the USDA test weight procedure a large weight of sample is used, e.g., about 700 to 1,000 grams. Since the accuracy of most high quality scales is independent of the weight placed on the scale and scale accuracy in the grain industry is normally about 0.1 gram, any error of 0.1 gram is negligible when compared to the 700 to 1,000 grams of grain.
Errors in measuring height accurately are magnified if one uses a small diameter container. For example, assuming a two-inch circular cylinder with a height of grain of about four inches determined by optical techniques with a possible error of 0.1 inch and assume that the grain weighs 40 grams, the possible error will calculate to a 2.5% error which is more than 10 times that allowable under the official USDA procedure. It is believed that this is the principal reason that optical height measurement has not previously been used for test weight determination. Note, that for larger grains such as corn the possible error might be three to five times larger than the above example.
Errors due to the need for consistent compaction are not related to the accuracy of the height measurement. An instrument known in the art made by Dickey-John Corp. includes a small sample cup, about two inches in diameter and four inches deep. This cup after being filled is leveled off with a solenoid-actuated leveling device, and by weighing the empty and full cup, test weight is calculated. The Dickey-John system, however, does not provide the required accuracy, and the reason is thought to be based on how the cup is filled with grain, i.e., the grain is compacted into the cup in varying amounts and this variation in compacted weight is perhaps ten times higher than the allowable tolerance by the USDA.
Also known in the art and commonly available on the market for use in the agricultural sector of the economy are near infrared instruments for measuring protein, moisture and oil in grain products. Such instruments, such as the Trebor 90 made by Trebor Industries, Inc. in Gaithersburg, MD, allows an unskilled user to determine the protein, moisture and oil constituents of a grain sample in a few seconds. In performing such measurement a quantity of grain is poured into the Trebor 90 hopper and near infrared energy is passed through the sample while it is in a column below the hopper. The operation is further disclosed in U.S. Pat. No. 4,286,327. There is a need in the field to allow the same unskilled user who determines the protein, moisture and oil constituents utilizing the Trebor 90 to also automatically determine the test weight per bushel of the same grain whose chemical constituents are being tested. It would also be highly desirable to eliminate the requirement for a separate test and test instrument to determine the test weight per bushel of grain.